High capacity regenerable graphene-based sorbent

ABSTRACT

A process of removing a volatile organic compound (VOC) from a gaseous environment, involving contacting a gaseous feedstream containing one or more VOC&#39;s, such as an odoriferous compound, an irritant, a contaminant or pollutant, for example, formaldehyde, with a sorbent under conditions sufficient to reduce the concentration of the VOC&#39;s in the gaseous feedstream. The sorbent is comprised of a functionalized graphene prepared by amination of graphene oxide. The sorbent is regenerated by adsorbate desorption under mild conditions of air flow. The process can be run through multiple adsorption-desorption cycles in a single fixed bed or swing bed configuration, and is applicable to purifying indoor air and ventilation air as well as reducing pollutants in industrial waste gas streams.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/582,813, filed May 1, 2017, now allowed, which claims the benefit ofU.S. Provisional Patent Application Ser. No. 62/342,240, filed May 27,2016.

GOVERNMENT RIGHTS

This invention was made with support from the U.S. government underContract No. EP-D-15-040, sponsored by the Environmental ProtectionAgency. The U.S. Government holds certain rights in this invention.

FIELD OF THE INVENTION

In one aspect this invention pertains to a process of removing volatileorganic compounds, hereinafter “VOC's”, from a gaseous environment. Morespecifically, this invention pertains to a process of removing VOC'sfrom a gaseous environment, such as air, wherein the process employs ananocarbon material as a sorbent, more specifically, a graphene-basednanocarbon material. For purposes of this description, VOC's includeodoriferous compounds, skin and eye irritants, contaminants andpollutants. Contaminants and pollutants include a wide variety ofchemical compounds, such as formaldehyde, chlorocarbons, and aromaticcompounds, whose harmful effects on human health are well documented.Accordingly, the process and composition of this invention provideutility in cleaning air and waste gas streams of unpleasant as well asharmful VOC's.

BACKGROUND OF THE INVENTION

Public policy concerns are growing, especially in the United States,regarding indoor air quality and its impact on human health. Currently,ventilation air (also called “make-up air”) is needed to maintainacceptable concentrations of indoor-generated air pollutants. Generally,ventilation air must be conditioned prior to use, such conditioning toinclude subjection to particle filtration, heating or cooling, andhumidification or dehumidification as determined by daily weather andseasonal climate conditions. An estimated 20 to 40 percent of energyconsumption in buildings goes into conditioning indoor air, much of itdirected to treatment of the ventilation air.

Along similar lines, public policy and environmental concerns continuewith respect to outdoor air quality and atmospheric pollution. Waste gasstreams from industrial processes generate pollutants in quantities thatoften do not meet air pollution regulations. Accordingly, national lawsrequire treating industrial waste gases to reduce concentrations ofpollutants prior to disposing waste gases into the atmosphere; and suchlaws might become more stringent in the future.

Prior art in this area of technology discloses sorbents for pollutantsfrom indoor and industrial sources, such sorbents including activatedcarbon, expanded graphite, zeolites and molecular sieves. A majority ofgaseous pollutants including polar volatile organic compounds, indoorformaldehyde being one notable example, are weakly adsorbed by activatedcarbons. Consequently, polar VOC's are removed via chemical reactionwith compounds added to the activated carbon, or more typically, are notremoved but diluted with ventilation air to acceptable concentrations.Furthermore, where the sorbent must remove several pollutants from thesame environmental gaseous source, activated carbon and zeolites sufferfrom competitive adsorption wherein easily adsorbed compounds replaceand outgas weakly adsorbed compounds. Activated carbons and zeolites arealso prone to loss of sorbent capacity and mass through oxidation andattrition during thermal regeneration. Regeneration of activated carbonsalso poses a fire hazard.

Zeolite sorbents are considerably more expensive than activated carbon,but have the advantage of being environmentally benign, non-flammableand thermally stable. Zeolite sorbents are favored for treatment ofwaste gases and for processes requiring frequent thermal regeneration. Azeolite, however, cannot provide any adsorption area for moleculeslarger than its pore size or molecules for which it does not haveaffinity, because a zeolite's adsorption properties towards specificmolecules depend heavily on its silicon to aluminum (Si/Al) ratio,cation type, pore structure and acidity. Furthermore, zeolites typicallycannot achieve high rates of adsorption for polar pollutants, such asformaldehyde, and preferentially retain water inside their poreslimiting sorption of polar VOC's, such that under a relative humiditytypical of indoor air in a range of about 40-55 percent, the retentioncapacity of zeolite sorbents is significantly reduced.

Carbon nanotubes (CNT's) are known to function as sorbents for removingorganic compounds from air, as disclosed in international patentapplication publication no. WO2012/070886 (Bioneer Corporation); or froma liquid or gas as disclosed in US application publication 2003/0024884(Petrik); or from an exhaust stream as disclosed in U.S. Pat. No.6,511,527 (Yang, et al.). CNT's are expensive and difficult to producein large scale as needed for commercialization. US applicationpublication 2006/0191835 discloses a hydrophobic, non-porous, andcarbonaceous nanostructured material, specifically graphene, as asorbent for contaminants including substituted hydrocarbons, organicsolvents, and acids. Such publications are silent with respect toregenerability of the sorbent, except for WO2012/070886 which disclosesregenerability of the sorbent by heating at a temperature equal to orhigher than a catalytic incineration temperature.

The art would benefit from discovery of an improved sorbent for use in aprocess of removing one or more volatile organic compounds from agaseous environment, such as air or industrial waste gas streams. Such asorbent should desirably provide an improved sorbent capacity,especially towards polar VOC's, as well as good thermal and attritionresistance, and improved regeneration capabilities at lowertemperatures, as compared with conventional present day sorbents.

SUMMARY OF THE INVENTION

In a first aspect, we have discovered a novel process of removing avolatile organic compound from a gaseous feedstream, comprisingcontacting the gaseous feedstream comprising an initial concentration ofthe volatile organic compound with a sorbent under conditions sufficientto produce an effluent stream comprising a reduced concentration of thevolatile organic compound, as compared with the initial concentration.Significantly, the sorbent employed in the process of our inventioncomprises a novel functionalized graphene prepared by a processcomprising, contacting graphene oxide with an amine of the formula NHR₂,wherein each R is independently selected from the group consisting ofhydrogen, C₁₋₅ alkyl, and C₁₋₅ aminoalkyl, the contacting occurringunder reaction conditions sufficient to produce the functionalizedgraphene.

In a second aspect, we have discovered a novel sorbent compositioncomprising a functionalized graphene prepared by a method comprising,contacting graphene oxide with an amine of the formula NHR₂, whereineach R is independently selected from the group consisting of hydrogen,C₁₋₅ alkyl, and C₁₋₅ aminoalkyl, the contacting occurring under reactionconditions sufficient to produce the functionalized graphene.

The aforementioned process of this invention employs a unique nanocarbonsorbent, specifically a functionalized graphene, which allows formarkedly improved sorbent capacity for VOC's and improved regenerabilityat lower temperatures, the latter resulting over time in less thermaldegradation and less attrition of the sorbent. Moreover, by varying thekind and degree of the functionalization on the graphene, the sorbentcan be tailored to specific target VOC's, such as target pollutants andcontaminants present in indoor and ventilation air and present inindustrial waste gas streams. Higher sorbent capacity and longer sorbentlifetime correlate with improved clean-up efficiency and bettercommercial prospects in terms of reduced sorbent and operational costs.

One utility for the process and composition of this invention involvescleaning indoor air; thus, our sorbent is envisioned to be adaptable topresent day heating, ventilation, and air conditioning systems (HVACsystems) in conjunction with existing particle filters to directly cleanindoor air while decreasing the requirement for costly outside airventilation. As mentioned hereinbefore, about 20 to 40 percent of energyconsumed in U.S. commercial and residential buildings is used for HVACconditioning. Any reduction in energy consumption and associated costswhile reducing the requirement for outside air ventilation beneficiallyfills a need in the art. In a related aspect, the process andcomposition of this invention can be employed in purifying air instand-alone room purification units, for example, as a drop-inreplacement for activated carbon. Another utility for the process andcomposition of this invention involves scrubbing waste gas streams fromindustrial processes. This application envisions drop-replacingconventional activated carbon scrubbers with the novel sorbent of thisinvention for increased sorbent capacity and sorbent lifetime.

The graphene-based sorbent of this invention advantageously exhibits anexcellent degree of regenerability after the sorbent is saturated orpartially saturated with VOC sorbate. Moreover, regeneration is simplyaccomplished by flushing the saturated or partially saturated sorbentwith dry air at ambient or slightly above ambient temperature. Thisregeneration procedure advantageously results in energy savings byminimizing a need for thermal regeneration at elevated temperatures,such as incineration temperatures, which consume more energy and haveassociated risks such as flammability of carbon.

Tests performed at higher humidity, up to fifty-five percent relativehumidity, on the graphene-based sorbent of this invention showed littleto no effect of water on the retention capacity for polar VOC's, animportant feature which allows for flexibility in operation. Often,higher humidity negatively affects removal of polar VOC's, particularlyformaldehyde, due to competitive adsorption. In this invention, theaforementioned humidity problem is significantly reduced if noteliminated. As a further advantage, the sorbent of this inventionbeneficially exhibited little to no effect in performance on exposure tocarbon dioxide, a ubiquitous component in the environment and more so inindustrial waste streams. Accordingly, carbon dioxide does not interferewith the sorption capacity of the sorbent of this invention.

We have discovered that the functionalized graphene sorbent of thisinvention provides superior performance due to its relatively highsurface area and specific chemistry, with added potential for lowmanufacturing costs in large-scale production. Our discovery furtheradvances the use of our functionalized graphene to overcome limitationsto air purification inherent in present day commercial sorbents, notablytheir loss of capacity due to competitive adsorption, inadequateregenerability, inability to handle multiple classes of contaminants,and low volumetric capacity. Further advantages in sorbent capacity canbe accrued by displacing the graphene-based sorbent of this inventiononto a variety of supports including fibers, foams, and meshes. Thecombined improvements in performance of the sorbent of this inventionoffer benefits heretofore unachieved.

DRAWINGS

FIG. 1 depicts a bar graph of sorbent capacity of an embodiment of thefunctionalized graphene sorbent of this invention, as used in theprocess of this invention and as compared with sorbent capacities ofalternative sorbent materials.

FIG. 2 depicts a graph of formaldehyde break-through as a function oftime for an embodiment of the process of this invention, as comparedwith a comparative process.

FIG. 3 depicts graphs of formaldehyde break-through as a function oftime for an embodiment of the process of this invention cycled throughfour adsorption-desorption cycles.

FIG. 4 depicts a bar graph of sorbent capacity of an embodiment of thefunctionalized graphene sorbent of this invention, as used in theprocess of this invention cycled through four adsorption-desorptioncycles.

FIG. 5 depicts graphs of formaldehyde desorption as a function of timefor an embodiment of the functionalized graphene sorbent of thisinvention, as observed during desorption cycles in the process of thisinvention.

FIG. 6 depicts bar graphs of sorbent capacity of an embodiment of thefunctionalized graphene sorbent of this invention, as used in theprocess of this invention through four adsorption-desorption cycles atincreased relative humidity.

FIG. 7 depicts graphs of formaldehyde breakthrough as a function of timefor two cycles of the process illustrated in FIG. 6.

FIG. 8 depicts a graph of toluene breakthrough as a function of time foran embodiment of the process of this invention.

DETAILED DESCRIPTION OF THE INVENTION

In one preferred embodiment, this invention pertains to a novel processof removing a volatile organic compound from a gaseous feedstream,comprising contacting the gaseous feedstream comprising an initialconcentration of the volatile organic compound with a sorbent underconditions sufficient to produce an effluent stream comprising a reducedconcentration of the volatile organic compound, as compared with theinitial concentration. The sorbent employed in this preferred embodimentcomprises a novel nitrogen and oxygen-functionalized graphene preparedby a process comprising, contacting graphene oxide with an amine of theformula NHR₂, wherein each R is independently selected from the groupconsisting of hydrogen, C₁₋₅ alkyl, and C₁₋₅ aminoalkyl, the contactingoccurring in the absence of a carbon nanotube and occurring underreaction conditions sufficient to produce the nitrogen andoxygen-functionalized graphene.

In a second preferred embodiment, this invention pertains to a novelsorbent composition comprising a nitrogen and oxygen-functionalizedgraphene prepared by a method comprising, contacting graphene oxide withan amine of the formula NHR₂, wherein each R is independently selectedfrom the group consisting of hydrogen, C₁₋₅ alkyl, and C₁₋₅ aminoalkyl,the contacting occurring in the absence of a carbon nanotube andoccurring under reaction conditions sufficient to produce the nitrogenand oxygen-functionalized graphene.

In yet another preferred embodiment, this invention pertains to a novelsorbent composition comprising a nitrogen and oxygen-functionalizedgraphene prepared by a method comprising: (a) contacting graphene oxidewith an amine of the formula NHR₂, wherein each R is independentlyselected from the group consisting of hydrogen, C₁₋₅ alkyl, and C₁₋₅aminoalkyl, the contacting occurring in the absence of a carbon nanotubeand occurring under reaction conditions sufficient to produce thenitrogen and oxygen-functionalized graphene; and (b) supporting thenitrogen and oxygen-functionalized graphene on a metal mesh substratehaving an ultra-short channel length.

The gaseous feedstream fed to the process of this invention encompassesany gaseous mixture comprising at least one volatile organic compound(VOC) and at least one other gaseous component. For the purposes of thisinvention, the term “volatile organic compound” is defined to includeany chemical compound comprising carbon and hydrogen that has ameasurable vapor pressure at ambient temperature and pressure, taken asabout 22° C. and about 1 atmosphere (101 kPa). The source of the gaseousfeedstream includes in one embodiment indoor air, in another embodimentoutdoor air, in yet another embodiment an industrial waste gas streamfrom any chemical or combustion process. The indoor air may derive fromthe air within residential and commercial buildings or any otherenclosed environment including cabin air as found in an aircraft orspaceship or submarine.

The volatile organic compound is typically present in the gaseousfeedstream in a concentration ranging from several parts per billion byvolume (ppb_(v)) to many thousands of parts per million by volume(ppm_(v)). Generally, the concentration depends upon the source of thegaseous environment or stream and VOC partial pressure therein. In oneembodiment, the volatile organic compound is present as an odoriferouscompound, irritant, pollutant or contaminant in air in a concentrationranging from greater than about 1 ppb_(v) to less than about 100ppm_(v), which even at these low concentrations may not satisfyenvironmental air quality laws. In another embodiment, the volatileorganic compound is present in an industrial waste gas stream in aconcentration ranging from greater than about 50 ppm_(v) to less thanabout 10,000 ppm_(v) (1 volume percent).

The volatile organic compound may be classified as either polar ornon-polar. For purposes of this invention, the term “polar” refers to achemical compound having a dipole moment of at least about 0.8 Debye(≥0.8 D); whereas the term “non-polar” refers to a chemical compoundhaving a weak dipole moment or no dipole moment, specifically, a dipolemoment less than 0.8 D including as low as 0 D. As known in the art,dipole moment is a measure of the electrical polarity of a system ofelectrical charges. Atoms that provide a dipole moment to a volatileorganic compound include, but are not limited to, oxygen, nitrogen,halogen, and sulfur. Suitable non-limiting examples of oxygen-containingsubstituents that impart a dipole moment to the VOC include hydroxyl,epoxy, acyl, and carboxyl. Suitable non-limiting examples ofnitrogen-containing substituents include amine and amide. Suitablenon-limiting examples of halogen-containing substituents includefluorine, chlorine, bromine, and iodine; and suitable non-limitingexamples of sulfur-containing substituents include thiol, sulfite,sulfate, and thionyl. Purely organic substituents consisting of hydrogenand carbon atoms can also provide a dipole moment to the volatileorganic compound depending upon position(s) and number of organicsubstituent(s), such organic substituents including but not limited tomethyl, ethyl, propyl, and higher homologues thereof.

In one embodiment, the volatile organic compound is a polar compoundhaving a dipole moment of at least about 1.5 D. In another embodiment,the volatile organic compound is a polar compound having a dipole momentof at least about 2.0 D. In yet another embodiment, the volatile organiccompound is a polar compound having a dipole moment of at least about2.5 D. At the upper limit the polar VOC typically has a dipole momentless than about 15 D.

The volatile organic compound in one embodiment comprises an odoriferouscompound, or an irritant, for example, an irritant towards skin and/oreyes. In another embodiment the volatile organic compound comprises apollutant or contaminant, which we define as a chemical compound that isclassified as noxious, hazardous or otherwise harmful to humans in aconcentration greater than an established threshold level. Reference ismade herein to the “Toxic and Hazardous Substances” List, Table Z-1, ofthe Occupational Safety and Health Standards, distributed by theOccupational Safety and Health Administration (OSHA), where the skilledperson finds a list of contaminants and pollutants, many of themclassifying as polar VOC's, along with their maximum allowableconcentration in air. Reference is also made to the “Priority PollutantList” distributed by the Environmental Protection Agency of the UnitedStates, wherein over 126 pollutants are identified. Among these listsare found various non-limiting examples of VOC's including acetaldehyde,acetic acid, acetone, acetonitrile, acrolein, acrylamide, acrylonitrile,allyl alcohol, allyl chloride, aminoethanol, aniline, benzyl chloride,butane thiol, butyl alcohol, butyl amine, chloroacetaldehyde,chlorobenzene, chloroform, cyclohexanol, dichlorobenzene,dichloromethane, dimethylamine, dihydroxymethane, dioxane, ethanethiol,ethyl acetate, ethylamine, formaldehyde, formic acid, methyl mercaptan,methyl acetate, methyl acrylate, methyl bromide, methyl ethyl ketone,phenol, propylene oxide, tetrahydrofuran, and vinyl chloride. It shouldbe appreciated that certain VOC's may be classified into several of theaforementioned categories; for example, an odoriferous VOC or irritantmay also be classified as a pollutant or hazardous material.Additionally, it should be appreciated that in another embodiment thegaseous feedstream comprises a mixture of such VOC's.

In one embodiment the volatile organic compound is selected from thegroup consisting of C₁₋₈ oxy-substituted hydrocarbons and C₁₋₈halocarbons and mixtures thereof. Preferred non-limiting examples ofC₁₋₈ oxy-substituted hydrocarbons include C₁₋₈ aldehydes, epoxides,alcohols, carboxylic acids, and mixtures of the aforementioned compoundshaving from 1 to 8 carbon atoms. In another preferred embodiment, thevolatile organic compound is a C₁₋₈ aldehyde or a mixture of C₁₋₈aldehydes, such as formaldehyde, propianaldehyde, and butyraldehyde. Inyet another preferred embodiment, the volatile organic compound isformaldehyde. Suitable non-limiting examples of C₁₋₈ halocarbons includeC₁₋₈ chlorocarbons, such as carbon tetrachloride, C₁₋₈hydrochlorocarbons, such as methylene dichloride, and C₁₋₈fluorochlorocarbons, such as fluorotrichloromethane.

In addition to the one or more volatile organic compounds, the gaseousfeedstream fed to the process of this invention comprises one or moreother gases, these including chemical compounds that are not harmful tohumans and chemical compounds that may be harmful but do not qualify asa VOC. In one embodiment, the other gases in the feedstream include atleast one naturally occurring gas including but not limited to molecularoxygen, nitrogen, water, carbon dioxide, noble gases (helium, neon,argon, krypton, xenon), or any mixture thereof as found, for example, inair. In another embodiment, the other gases in the feedstream includewaste gases produced by combustion, which comprise water, carbonmonoxide, carbon dioxide, or any mixture thereof.

The relative humidity of the gaseous feedstream fed to the process ofthis invention ranges from 0 percent to less than about 80 percent,relative humidity being taken as a percentage of water present in thefeedstream as compared with a maximum amount of water needed to saturatethe feedstream at a standard temperature and pressure, herein taken as22° C. and 1 atmosphere (101 kPa). A preferred relative humidity of thegaseous feedstream ranges from about 35 to about 70 percent for outdoorair and from about 40 percent to about 50 percent for indoor air.

We have discovered that the sorbent of this invention is essentiallynon-responsive to carbon dioxide and further that carbon dioxide hasessentially no adverse effects on the sorbent. Accordingly, the gaseousfeedstream in one embodiment comprises any concentration of carbondioxide less than 100 volume percent. Consequently, the sorbent of thisinvention beneficially provides for full use of its capacity towardssorbing VOC's without undesirable loss of capacity towards carbondioxide sorption.

We have also discovered that the novel sorbent employed in the processof this invention can be prepared generally by contacting graphene oxidewith an amine of the formula NHR₂, wherein each R is independentlyselected from the group consisting of hydrogen, C₁₋₅ alkyl, and C₁₋₅aminoalkyl, the contacting occurring under process conditions sufficientto prepare a functionalized graphene, more specifically, a nitrogen andoxygen-functionalized graphene. At the start, it should be appreciatedthat graphene comprises a 2-dimensional crystalline allotrope of carbonin which carbon atoms are densely packed in a regular array ofsp²-bonded, atomic scale hexagonal pattern. Graphene can be described asa one-atom thick layer of graphite, as disclosed by H. Schniepp et. al.in “Functionalized Single Graphene Sheets Derived from SplittingGraphite Oxide,” The Journal of Physical Chemistry B, Vol. 110, 17,2006, 8535-8539. Graphene functionalized with oxygen-bearingsubstituents is frequently referred to as “graphene oxide,” whichlikewise comprises a 2-dimensional crystalline allotrope of carbon inwhich carbon atoms are densely packed in a regular array of sp²-bonded,atomic scale hexagonal pattern. Graphene oxide, however, furthercomprises epoxy (/^(O)\) and hydroxyl (—OH) groups bonded to the surfaceof the graphene sheet as well as carboxyl [—C(O)OH] and hydroxyl (—OH)groups bonded to the edges of the sheet. Generally, the oxygen occurringas a mixture of hydroxyl, epoxy, and carboxyl substituents is present ina concentration greater than about 5 percent, preferably, greater thanabout 10 percent, by weight, based on the weight of the graphene oxide.Generally, the oxygen is present in a concentration less than about 40percent, preferably, less than about 30 percent, by weight, based on theweight of the graphene oxide. Of these, the carboxyl functionalityrepresents from 30 to 100 percent by weight of the total oxygen,depending upon how the graphene oxide is prepared.

From another perspective, the concentration of oxygen-containingsubstituents on the graphene oxide generally ranges from greater thanabout 5 oxygen-containing groups per 100 carbon atoms to less than about30 oxygen-containing groups per 100 carbon atoms. The proportion ofoxygen substituents converted to nitrogen-containing substituents istypically greater than 5 percent, preferably greater than about 15percent, and more preferably, greater than about 25 percent, up toessentially 100 percent.

The sorbent of this invention is prepared by first functionalizinggraphene with a plurality of the aforementioned oxygen-containingsubstituent(s), as known in the art, so as to form the graphene oxide,which also may be purchased commercially (e.g., from AngstronMaterials); and thereafter, a portion of the aforementionedoxygen-containing substituents is converted to one or more of thenitrogen-containing functionalities. More specifically, graphene oxideis solubilized or suspended in a suitable solvent and reacted with theamine of the formula NHR₂, wherein each R is independently defined asnoted hereinbefore, at a temperature sufficient to promote theappropriate substitution or thermochemical reaction of the amine withthe oxygen functionalities on the graphene. In one preferred synthesis,graphene oxide is reacted with aqueous ammonia (ammonium hydroxide) at atemperature ranging from about 50° C. to about 110° C. for a timeranging from about 5 hours to about 48 hours. The quantity of ammoniumhydroxide employed is usually sufficient to convert at least 10 percentand up to 100 percent of the oxygen functionalities to nitrogenfunctionalities. In another embodiment an excess of ammonium hydroxiderelative to oxygen functionalities is employed. Following the thermaltreatment, the solution is filtered and the resulting nitrogen andoxygen-functionalized graphene is thoroughly washed with water thendried at a temperature ranging from about 80° C. to 110° C. to obtainthe solid nitrogen and oxygen-functionalized sorbent of this invention.Where the amine (NHR₂) is an alkylamine or alkyldiamine, a suitablesolvent or diluent, such as water or C₁₋₃ alcohol, can be employed; orthe amine itself acts as the solvent; and the reaction conditions areclosely similar to those mentioned above as a person skilled in the artwill appreciate.

We believe, although such belief is theory and should not be limiting inany manner, that the amine (NHR₂) reacts with the hydroxyl and carboxylsubstituents on the graphene oxide giving rise, respectively, to amine(—NR₂) and amide [—C(O)NR₂] functionalities bonded to the graphene.Additionally, the amine may react with the epoxy substituents on thegraphene oxide giving rise to both hydroxyl (—OH) and amine (—NR₂)functionalities, although the epoxy groups are considered to be lessreactive than the hydroxyl and carboxyl groups. Accordingly, the sorbentof this invention comprises graphene functionalized with a plurality oftwo types of substituents: (a) an oxygen-containing substituent selectedfrom the group consisting of hydroxyl (—OH), epoxy (/^(O)\) and carboxyl[—C(O)OH], and mixtures thereof; and (b) a nitrogen-containingsubstituent selected from the group consisting of amine (—NR₂), amide[—C(O)NR₂], and mixtures thereof, wherein each R again is independentlyselected from hydrogen, C₁₋₅ alkyl, and C₁₋₅ aminoalkyl. It is howeverpossible that the sorbent also comprises ionic bonded amine in the formof quaternary ammonium carboxylates represented by [—C(O)O⁻⁺HNHR₂]. Notethat even in the instance wherein all hydroxyl, carboxyl, and epoxygroups have reacted with amine, the sorbent product will contain amine,amide, and hydroxyl groups providing for both nitrogen andoxygen-functionalization.

Generally, the nitrogen and oxygen-functionalized graphene sorbent ofthis invention has a particle size correlating substantially to theparticle size of the unmodified graphene oxide from which the sorbent isderived. Since the sorbent and the unmodified graphene oxide are bothessentially two-dimensional materials, the thickness of the particles issignificantly smaller than the width of the particles. As a guide, whengraphene oxide is modified as described hereinabove, the thickness ofthe resulting nitrogen and oxygen-functionalized graphene ranges fromabout 1 nanometer (1 nm) to less than about 50 nm, as determined bytransmission electron microscopy (TEM) or scanning electron microscopy(SEM). The width of the particles ranges from greater than about 100 nm,preferably, greater than about 200 nm, to less than about 10 microns(μm). Various conventional methods, such as ball-milling, sonication,and thermal annealing, can be employed to modify the size of theparticles and/or to select a range of desired particle sizes. Thenitrogen and oxygen-functionalized graphene sorbent of this inventiongenerally exhibits a surface area closely similar to the surface area ofthe graphene oxide starting material. A typical surface area ranges fromabout 100 m²/g to about 1,000 m²/g, preferably between about 300 m²/gand about 500 m²/g.

In another embodiment the sorbent of this invention further comprisesone or more catalytic metals, including for example metals capable ofcatalyzing oxidation reactions, such as the Group VIII metals of thePeriodic Table as well as copper and manganese (e.g., MnO₂). In anotherembodiment, the sorbent incorporates a bioactive material that canbiologically degrade the volatile organic compound after adsorption ontothe sorbent.

The sorbent of this invention is provided to the adsorption process inany of a variety of physical forms including but not limited to powders,pellets, extrudates, or as a layer, laminate or coating on a non-porousor macroporous support, such supports to include ceramic and metallicfibers, meshes, and foams. The term “macroporous” refers to pores,channels, or void spaces having a critical dimension larger than about0.5 micron (>0.5 μm), and preferably, larger than about 25 μm. In oneembodiment, the sorbent is provided as a layer or a coating covering asupport in the form of a wall or surface of the sorbent bed or pelletsor extrudates filling the bed. In another embodiment, the sorbent isapplied to a high surface area support, such as a support having asurface area of at least about 100 m²/g, for the purpose of increasingaccess of the gaseous feedstream to the sorbent as well as decreasingpressure drop across the sorbent bed. In yet another embodiment, thesorbent further comprises a binder, which functions to impart anacceptable degree of cohesiveness and attrition resistance to thesorbent. Supports and binders for sorbents and catalysts are known tothe person skilled in the art.

In yet another embodiment, the sorbent comprises a layer or coating ofthe nitrogen and oxygen-functionalized graphene sorbent on a highsurface area support comprising an ultra-short-channel-length mesh,preferably, a Microlith® brand ultra-short-channel-length metal meshavailable from Precision Combustion, Inc., North Haven, Conn. Adescription of the aforementioned mesh can be found in U.S. Pat. Nos.5,051,241, and 6,156,444, both patents incorporated herein by reference.Generally, the ultra-short-channel-length mesh is provided as a lowthermal mass monolith of ultra-short-channel-length, in contrast toprior art monoliths having longer channel lengths. For the purposes ofthis invention, the term “ultra-short-channel-length” refers to achannel length in a range from about 25 microns (μm) (0.001 inch) toabout 500 m (0.02 inch). Thus, in visual appearance the preferred meshof ultra-short-channel-length resembles a net or screen. In contrast,the term “long channels” pertaining to prior art monoliths refers tochannel lengths greater than about 5 mm (0.20 inch) upwards of 127 mm (5inches).

The loading of sorbent onto any support can be described in units ofweight sorbent per unit volume of support; and this advantageouslyranges from about 2 mg sorbent per cubic centimeter support (2 mg/cm³)to about 60 mg/cm³. This description takes gross dimensions of thesupport into account. The thickness and uniformity of the sorbentcoating on the support vary depending upon the specific support,sorbent, and coating method selected.

It should be appreciated that in one preferred embodiment, the nitrogenand oxygen-functionalized sorbent composition of this invention excludesany microporous and mesoporous co-sorbent, including any co-sorbentcarbon nanotube (CNT), zeolite, molecular sieve, activated carbon, ormixture thereof. Such co-sorbents typically contain a regular orirregular system of tubes, pores, channels, or void spaces having acritical dimension ranging from about 0.5 nanometer (0.5 nm) to about 50nm, which we find undesirable for two reasons. Firstly, such microporousand mesoporous co-sorbents are limited to trapping only VOC's that fitwithin their tubular or pore system, that is, those VOC's withdimensions smaller than the dimensions of the tubes, pores, channels, orvoid spaces. Secondly, VOC's that enter the tubular or pore system mayfind it difficult to exit. As a consequence, regenerating microporousand mesoporous co-sorbents is difficult resulting in undesirable loss insorbent capacity. Additionally, CNT's in particular are difficult tofabricate in large scale thereby adding unnecessary costs ofmanufacture. In contrast, our nitrogen and oxygen-functionalizedgraphene sorbent is prepared in one simple, cost effective step; isessentially non-porous (i.e., essentially does not contain pores andchannels), and shows excellent regenerability.

In terms of operation, in one embodiment the process of this inventionis conducted in a single sorbent bed where in adsorption mode a flow ofgaseous feedstream containing at least one VOC in an initialconcentration is contacted with the sorbent for a time during which aneffluent stream exiting the sorbent bed contains an acceptably reducedconcentration of the VOC. When the sorbent bed is fully or partiallysaturated and the effluent stream contains an unacceptable concentrationof the VOC (otherwise known as “break-through”), the flow of gaseousfeedstream to the bed is stopped. Thereafter, the sorbent is regeneratedby running the bed in desorption mode either by heating the sorbent bed,or by decreasing pressure, e.g., pulling a vacuum on the sorbent bed, orby passing a sweep gas through the sorbent bed at selected temperatureand pressure to drive off the adsorbed VOC, which is typically collectedin a containment vessel or exhausted into an exterior atmosphere.Suitable sweep gases include air, nitrogen, carbon dioxide, helium,argon, and the like, with air being a preferred sweep gas. Thereafter,the process involves alternating the sorbent bed between adsorption anddesorption modes over many reiterations. In one embodiment, regenerationis accomplished by exposing the sorbent to a high space velocity flow ofair at room temperature.

In another embodiment a plurality of sorbent beds is engaged in swingmode operation such that one or more sorbent beds are operated inadsorption mode, while one or more other sorbent beds are simultaneouslyoperated in desorption mode. As the beds operating in adsorption modereach the desired partial or full saturation, the bed operations areswitched such that the bed(s) originally operating in adsorption modeare engaged in desorption mode, while the bed(s) originally operating indesorption mode are converted to adsorption mode. Temperature swingoperation involves cycling the beds between a temperature suitable foreffecting adsorption and a temperature, usually a higher temperature,suitable for effecting desorption. Pressure swing operation involvescycling the beds between a pressure gradient, for example, exposure tothe VOC at normal pressure to effect adsorption and exposure to a vacuumto effect desorption. Swing bed technology is known in the art andadvantageous in eliminating downtime while a bed is regenerated.

Valves for directing the flow(s) into and out of each sorbent bed can beany of those commercially available flow control valves known to aperson skilled in the art. Likewise, valves for exposing each sorbentbed to a pressure gradient include any of such pressure control valvesthat are known to a skilled person and generally available commercially.The term “pressure gradient” means that the pressure control valveconnects two environments at different pressure; for example, thepressure of the contaminant in the sorbent bed when the bed is loadedmay be higher than the pressure of the contaminant in an environmentoutside the sorbent bed. Accordingly, the contaminant can be desorbedfrom the sorbent bed by opening the relevant valve and exposing thesorbent bed to a lower pressure environment. Sensors detecting aconcentration of the contaminant in each sorbent bed or in an effluentstream from each sorbent bed can be any commercially available sensorsuitable for detecting the contaminant of interest. Such sensorsinclude, for example, flame ionization detectors and thermalconductivity detectors. Finally, the controller responsive to thesensor(s) or a predetermined time period for controlling operation ofthe plurality of valves can be obtained commercially or constructed by aperson skilled in the art.

The adsorption-desorption process of this invention is conducted underany process conditions providing for acceptable removal or reduction ofthe one or more VOC's from the gaseous feedstream. Specific processconditions are determined by the selected VOC and heat and mass balanceconsiderations. The following process conditions are presented forguidance purposes; however, other process conditions may be operable andmore desirable depending upon the specific VOC(s). The adsorption cycleis operated advantageously at a sorbent bed temperature ranging fromabout 5° C. to about 50° C. and a pressure ranging from about 1 atm (101kPa) to about 5 atm (506 kPa). In a preferred embodiment, the adsorptioncycle is operated at ambient temperature and pressure, taken as 22° C.and 1 atm (101 kPa). Advantageously, during the adsorption cycle thegaseous feedstream containing the one or more volatile organic compoundsis fed to the sorbent bed at a gas hourly space velocity ranging fromabout 100 ml total gas flow per ml sorbent bed per hour (hr⁻¹) to about100,000 hr⁻¹. The desorption cycle is beneficially operated at atemperature ranging from about ambient, taken as 22° C., to about 200°C., but preferably operates between ambient and about 50° C.Advantageously, the desorption cycle is operated at a total pressureranging from about 0.0005 atm (0.05 kPa) to about 1 atm (101 kPa).Typically, each regeneration cycle recovers more than 50 percent of theprevious cycle's sorbent capacity.

In adsorption mode, the process of this invention achieves a lowerconcentration of VOC's in the effluent stream exiting the sorbent bed(s)as compared with the concentration of VOC's in the feedstream fed to thebed. Generally for air ventilation applications the concentration ofeach contaminant or pollutant VOC in the effluent stream isadvantageously less than about 50 parts per million by volume (ppm_(v)),preferably, less than about 25 ppm_(v), more preferably, less than about1 ppm_(v), and most preferably, less than about 100 parts per billion byvolume (ppb_(v)), based on the total volume of the effluent streamexiting the adsorption bed. Generally, for smoke stack or industrialprocess applications, the concentration of each contaminant in theeffluent stream is less than about 8,000 parts per million by volume(ppm_(v)), preferably, less than about 5,000 ppm_(v), more preferably,less than about 500 ppm_(v), even more preferably, less than about 50ppm_(v), even more preferably, less than about 10 ppm_(v), and mostpreferably, less than the minimum detectable concentration.

One important characteristic of the novel sorbent of this inventionshould be fully appreciated for distinguishing our novel sorbent fromsorbents already known in the art. Specifically, the sorbent of thisinvention exhibits excellent regenerability under very mild conditions,namely, under a flow of a sweep gas at ambient temperature (22-25° C.)and ambient pressure (about 101 kPa). This allows for our sorbent to beregenerated at ambient conditions with clean air, i.e., air containing anon-detectable concentration of any pollutant or contaminant. We havefurther discovered that our sorbent can be cycled through at least about4 adsorption-desorption cycles without losing more than 20 percent ofits original capacity, when the sorbent is provided as a powder. Incontrast, sorbents of the prior art typically require thermalregeneration at temperatures considerably higher than ambienttemperature.

EMBODIMENTS Example 1 (E-1)

A rig for adsorption and desorption testing was constructed as follows.A single fixed sorbent bed comprising a cylindrical tube [stainlesssteel, 1.5 inch inner dia. (3.8 cm), 10 inch length (2.5 cm)] was fittedat each end with a flow line and conventional flow control valves, onthe upstream end for controlling a flow of gaseous feedstream into thebed and on the downstream end for exiting an effluent flow from the bed.The tube was provided with a voltage controller and wrapped with aheating tape so as to provide heating to the bed. A humidity control wasconnected to the upstream flow line to provide gaseous water to thefeedstream. The downstream effluent line was connected to a gaschromatograph and a formaldehyde detector (Interscan Corp., RM Series).

A sorbent (700 mg) of nitrogen and oxygen-functionalized graphene wasemployed, which ensured no by-pass or channeling of contaminated airthrough the sorbent bed. The sorbent was prepared by thermal treating acommercial graphene oxide with aqueous ammonium hydroxide as follows.The graphene oxide powder (Angstron Materials, catalog number N002-PDE)compri sed a few-layer graphene oxide platelets with a thickness of 2-3nanometers (2-3 nm); a lateral dimension of approximately 7 micrometers(7 μm); a carbon content of 60-80 percent; oxygen content between 10-30percent; and a surface area of 420 m²/gm.

The graphene oxide powder was mixed in a flask with excess aqueousammonium hydroxide (30 wt. percent solution) in a ratio of 30 g ammoniumhydroxide solution per gram graphene oxide. The mixture was heated to90-100° C. under reflux for 48 h. Periodically, the level of the mixturewas checked and replenished as needed, as some ammonia gas was releasedfrom solution under the reaction conditions. At the end of the 48 h asolid product was recovered by filtration, and the solid was washed withdeionized water until the pH of the filtrate was measured at neutral.The solid was further dried at 70° C. overnight to yield the sorbent ofthis invention as a powder.

A contaminant gas comprising air and formaldehyde (30 ppm, Air LiquidSpecialty Gases) was diluted with uncontaminated air in a quantitysufficient to deliver a feedstream mixture comprising air andformaldehyde (10 ppm) to the sorbent bed. The formaldehyde concentrationof 10 ppm was chosen to ensure a relatively fast break-through fortimely analysis. Although OSHA's short-term exposure limit forformaldehyde is no greater than 2 ppm total over 15 minutes, we chose ahigher concentration to ensure that the break-through was sufficientlyfast to allow for multiple experiments within an acceptable time frame.

Operating conditions during adsorption mode were as follows: inletpressure of the feedstream to the sorbent bed, 2-3 psig (14-21 kPa);temperature of the sorbent bed, ambient, taken as 22° C.; flow rate,0.75 standard liters contaminated air per minute; relative humidity ofthe contaminated air, 10 percent. Break-through was defined as the pointat which the concentration of formaldehyde in the effluent streamequaled 50 percent of the inlet formaldehyde concentration, namely, 5ppm. Note that conditions under which our apparatus was tested were notoptimized for mass transfer from the contaminated air to the sorbent.Supporting the sorbent on a higher surface area substrate, such aspellets or metal mesh rather than providing the support as a powder, isexpected to increase sorbent capacity.

FIG. 1 depicts a bar graph of the capacity of the functionalizedgraphene sorbent for formaldehyde. Under the test conditions the sorbentcapacity was 0.32 mmoles CH₂O/g sorbent. FIG. 2 depicts a graph offormaldehyde break-through as a function of time. It was found thatformaldehyde break-through occurred at about 650 minutes.

Comparative Experiment 1 (CE-1 (a-e))

For comparative purposes, the process of Example 1 was repeated fivetimes, each time with the exception that the nitrogen andoxygen-functionalized graphene sorbent of Example 1 was replaced with acomparative sorbent material, specifically the following: (1a)multi-layer graphene (Angstron Materials, 40 m²/g)); (1b) graphene oxide(Angstron Materials, 400 m²/g); (1c) graphene oxide functionalized withC₈-alkylamide substituents, prepared from graphene oxide using thionylchloride reaction followed by reaction with octylamine; (Id) activatedcarbon (Spill X, 1,400 m²/g); and (1e) zeolite Y (Sigma-Aldrich, 600m²/g).

FIG. 1 depicts a bar graph of the sorbent capacity of each of thecomparative sorbents for formaldehyde. It was found that under the testconditions the sorbent capacity was considerably less for each of thecomparative sorbents: multi-layer graphene, graphene oxide,C_(g)-alkylamide functionalized graphene oxide, activated carbon, andzeolite Y, as compared with the sorbent of this invention exemplified inE-1.

FIG. 2 depicts a graph of formaldehyde break-through as a function oftime for the zeolite Y comparative sorbent, which was the best of thecomparative sorbents. It was found that formaldehyde break-throughoccurred at about 380 minutes, which was a considerably shorter timethan that observed for the sorbent of this invention exemplified in E-1.

Example 2 (E-2)

The process of the invention was evaluated under conditions of multipleadsorption-desorption cycles for the purpose of evaluating regenerationcapacity of the sorbent of the invention exemplified in E-1. Theapparatus and test conditions were similar to Example E-1 with someexceptions. In order to achieve faster formaldehyde break-through toachieve multiple adsorption-desorption cycles within a reasonable timeframe, the formaldehyde concentration in air was decreased from 10 ppmas used in E-1 to 7.5 ppm for this example. In addition, the spacevelocity of the contaminant feedstream was increased from 0.75 slpm asused in E-1 to 1.4 slpm in this example. The amount of sorbent wasdecreased from 700 mg as used in E-1 to 100 mg in this example. Thesemodifications of the test method ensured contaminant break-throughwithin approximately 1 h allowing for a more rapid testing procedure.Break-through was again defined as the point at which the outletcontaminant concentration increased to 50 percent of the original inletcontaminant concentration. During the adsorption cycle, pressure andtemperature test conditions were similar to those used in E-1. Eachdesorption (regeneration) cycle was effected by flushing the sorbentwith clean air. The flow rate, pressure, temperature, and time of thedesorption cycles are presented for each desorption cycle in Table 1.

TABLE 1 Regeneration Test Matrix Air flowrate, Pressure, Temperature,Time, Cycle slpm kPa ° C. min 1 1.4 20.7 25 210 2 1.4 20.7 25 210 3 1.420.7 25 210

FIG. 3 depicts formaldehyde break-through curves over fouradsorption-three desorption cycles under the desorption conditions ofTable 1. FIG. 4 depicts bar graphs of sorbent capacity from cycles 1through 4. FIG. 5 depicts desorption curves plotting formaldehydeconcentration in the effluent stream versus time for pre-cycles 2 and 3and post-cycle 4. From cycles 1 to 2 we observed a decrease ofapproximately 23 percent in sorbent capacity; however, the sorbentcapacity stabilized over subsequent cycles 2 to 4. The change in sorbentcapacity from first to second cycles is believed to be in part due tosettling of the sorbent powder under fixed bed testing conditions andgas flow channeling. Desorption of formaldehyde from the sorbentoccurred at room temperature.

Example 3 (E-3)

The process of E-1 was repeated with the exception that the testconditions were as follows: 7.5 ppm formaldehyde in air; 1.4 slpm flowof contaminated air; and relative humidity increased from 10 percent to40 percent. For the increased humidity, an aqueous solution offormaldehyde (37 wt. percent in water stabilized with 10-15 wt. percentmethanol) was dispersed in an air stream with a syringe pump to yieldthe target inlet concentration of formaldehyde and water. The testemployed the same pressure, temperature, and space velocity parametersas for the adsorption cycle used in E-1. The process was run throughfour adsorption-desorption cycles. Regeneration was effected at roomtemperature for cycles 2 and 3 and thermally at 150° C. for cycle 4.

Results are shown in FIG. 6 and FIG. 7. In cycle 1, as shown in FIG. 6,approximately the same capacity was measured at 40 percent relativehumidity (0.0.25 mmol/g sorbent) as compared with the 10 percentrelative humidity of E-1 (0.3 mmol/g sorbent). As seen, only 50 percentof the original sorbent capacity was recovered with room temperature airregeneration (cycles 2 and 3), while thermal regeneration at 150° C.(cycle 4) recovered approximately 70 percent of the original capacity.Formaldehyde is highly soluble in water; and water can also adsorb onthe graphene surface. Thus, a certain degree of thermal regenerationappears to be beneficial under high humidity conditions to effectregeneration of the sorbent. Although at room temperature only 50percent of the original sorbent capacity was recovered, this capacitywas completely regenerated between cycles 2 and 3 indicating that postcycle 1 humidity driven capacity loss, a high degree of sorbentregenerability is achievable at room temperature. FIG. 7 illustratesformaldehyde breakthrough curves for Cycles 1 and 4.

Example 4 (E-4)

The sorbent of Example 1 was evaluated for sorbent capacity for toluene.The test rig of Example 1 was operated under the following conditions:700 mg sorbent under a flow (0.75 SLPM) of air contaminated with toluene(100 ppm_(v)) at room temperature. Breakthrough was considered when theconcentration of toluene at the outlet reached 50 percent of the inletconcentration (50 ppm_(v)). The sorbent capacity was observed to be 0.5mmol toluene/g sorbent. A breakthrough curve is illustrated in FIG. 8.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions, or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. A process of removing a volatile organic compound from a gaseousfeedstream, comprising contacting the gaseous feedstream comprising aninitial concentration of the volatile organic compound with a sorbentunder adsorption conditions sufficient to produce an effluent streamcomprising a reduced concentration of the volatile organic compound, ascompared with the initial concentration; wherein the sorbent comprises afunctionalized graphene prepared by a process comprising reactinggraphene oxide with an amine of the formula NHR₂, wherein each R isindependently selected from the group consisting of hydrogen, C₁₋₅alkyl, and C₁₋₅ aminoalkyl, the reacting occurring under conditionssufficient to produce the functionalized graphene.
 2. A process ofremoving a volatile organic compound from a gaseous feedstream,comprising contacting the gaseous feedstream comprising an initialconcentration of the volatile organic compound with a sorbent underconditions sufficient to produce an effluent stream comprising a reducedconcentration of the volatile organic compound, as compared with theinitial concentration; the sorbent comprising a nitrogen andoxygen-functionalized graphene prepared by a process comprisingcontacting graphene oxide with an amine of the formula NHR₂, whereineach R is independently selected from the group consisting of hydrogen,C₁₋₅ alkyl, and C₁₋₅ aminoalkyl, the contacting occurring in the absenceof a carbon nanotube and occurring under reaction conditions sufficientto produce the nitrogen and oxygen-functionalized graphene.
 3. Theprocess of claim 2 wherein the gaseous feedstream comprises air, and thevolatile organic compound is an odoriferous compound, or irritant, orpollutant or contaminant in a concentration greater than 10 ppb_(v) andless than 100 ppm_(v).
 4. The process of claim 2 wherein the gaseousfeedstream comprises a waste gas stream from an industrial process, andwherein the volatile organic compound has a concentration in the wastegas stream of greater than 500 ppm_(v) and less than 10,000 ppm_(v). 5.The process of claim 2 wherein the volatile organic compound is a polarvolatile organic compound having a dipole moment equal to or greaterthan 0.8D.
 6. The process of claim 2 wherein the volatile organiccompound is selected from C₁₋₈ oxy-substituted hydrocarbons and C₁₋₈halocarbons.
 7. The process of claim 6 wherein the volatile organiccompound is formaldehyde.
 8. The process of claim 2 wherein the aminereacting with the graphene oxide is aqueous ammonia (ammoniumhydroxide).
 9. The process of claim 2 wherein the contacting of thegaseous feedstream with the sorbent is conducted at a temperatureranging from 5° C. to 50° C. and a pressure ranging from 1 atm (101 kPa)to 5 atm (506 kPa).
 10. The process of claim 2 wherein the gaseousfeedstream further comprises carbon dioxide.
 11. The process of claim 2wherein the gaseous feedstream has a relative humidity ranging from 0percent to less than 80 percent.
 12. The process of claim 2 whereinafter the sorbent is saturated or partially saturated with the volatileorganic compound, the process further comprises the step of desorbingthe volatile organic compound; and thereafter the steps of adsorbing anddesorbing are reiterated one or more times.
 13. The process of claim 2wherein the desorbing is effected by heating the sorbent, or by exposingthe sorbent to a pressure gradient, or by passing a sweep gas throughthe sorbent.
 14. The process of claim 13 wherein the desorbing iseffected by passing a flow of air through the sorbent at a temperatureranging from 22° C. to less than 50° C.
 15. The process of claim 2wherein the contacting is conducted in a single fixed sorbent bed orconducted in a plurality of sorbent beds operating in swing mode. 16.The process of claim 2 wherein the sorbent is supported on a metal meshsubstrate having an ultra-short-channel-length.
 17. The process of claim2 wherein the effluent stream comprises air or a waste gas streamcontaining a volatile organic compound in a concentration less than 50ppm_(v).